Electric axial flow pump

ABSTRACT

An electric axial flow pump comprising:  
     a stator  6  having a field coil  10,  a rotor  3  including a cylindrical hollow shaft  4  having open ends surrounded by the stator and a plurality of magnets  5  fixed around the hollow shaft, and a flow generation section  2  fixed inside the hollow shaft for rotating integrally with the rotor when the field coil is excited, thereby generating flow of a fluid  15  inside the hollow shaft.

CLAIM OF PRIORITY

The present application claims priority from Japanese application serial No. 2006-198947, filed on Jul. 21, 2006, the content of which is hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric axial flow pump having a stator and a rotor.

2. Prior Art

The electric axial flow pump is widely used such as a vacuum pump for sucking electronic parts used in an electronic part mounting device and a circulating pump for circulating cooling water in a cooling circuit used in an automobile and a portable personal computer.

When using the electric axial flow pump as a vacuum pump, there is a case that the electric axial flow pump and a suction section for directly sucking electronic parts are installed separately from each other and an auxiliary section such as a pipe for connecting the electric axial flow pump and suction section is necessary. The reason that the electric axial flow pump and suction section are installed separately from each other is conceivably that the volume of the electric axial flow pump is large. Therefore, a motor having a built-in pump excluding an auxiliary section such as a pipe which is realized by mounting an electric axial flow pump in a suction section rotated by a motor is proposed (for example, refer to Patent Document 1). To mount the electric axial flow pump on the suction section, further miniaturization of the electric axial flow pump is desired.

Further, also with respect to the circulating pump, since the cooling circuit and furthermore an automobile and a portable personal computer are designed according to the volume of the electric axial flow pump, from the viewpoint of enhancement of the degree of freedom of the design of an automobile and a portable personal computer, further miniaturization of the electric axial flow pump is desired. And, a fluidic pump in which the stator of the motor of the electric axial flow pump is described as a claw pole stator, thus the length of the motor in the direction of the rotary shaft is shortened is proposed (for example, refer to Patent Documents 2 and 3).

Patent Document 1: Japanese Patent Application Laid-open Publication No. 2005-220812 (Paragraphs 0020 to 0023, FIG. 2)

Patent Document 2: Japanese Patent Application International Publication No. 2003-505648 (Paragraph 0020, FIG. 2)

Patent Document 3: Japanese Patent Application International Publication No. 2003-515059 (Paragraph 0032, FIG. 3)

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide an electric axial flow pump able to be miniaturized.

To solve the aforementioned object, the present invention provides an electric axial flow pump including a rotor having a cylindrical hollow shaft having open ends which is arranged so as to be surrounded by a stator and a flow generation section which is fixed inside the hollow shaft, rotates integrally with the rotor when a field coil of the stator is excited, thereby generates flow of a fluid inside the hollow shaft.

According to the present invention, an electric axial flow pump capable of miniaturization can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIG. 1(a) is a side view of the electric axial flow pump relating to the first embodiment of the present invention and FIG. 1(b) is a cross sectional view in the direction A-A shown in FIG. 1(a), wherein to a flow generation section 2, a front view is applied to provide easy understanding,

FIG. 2 is a cross sectional view of the rotor of the electric axial flow pump in the vertical plane shown in the first embodiment of FIG. 1,

FIG. 3 is an exploded perspective view of the stator of the electric axial flow pump shown in the first embodiment of FIG. 1,

FIG. 4 is a perspective view of the stator including the cut section shown in the first embodiment of FIG. 1,

FIG. 5 is a bottom view of the first claw pole core or second claw claw core of the stator magnetic core of the stator shown in the first embodiment of FIG. 1,

FIG. 6 is a top view of the first claw pole core or second magnetic core of the stator magnetic core of the stator shown in the first embodiment of FIG. 1,

FIG. 7 is a cross sectional view in the direction B-B shown in FIG. 6,

FIG. 8 is graphs showing the magnetizing characteristics of the stator magnetic cores shown in the first embodiment of FIG. 1 prepared by various materials,

FIG. 9 is graphs showing the relationship between the number of claw poles and the output torque shown in the first embodiment of FIG. 1,

FIG. 10 is graphs showing the relationship between a ratio T/P of a mean width angle T of the maximum width angle and minimum width angle occupied by the claw pole in the peripheral direction of the stator magnetic core to a pitch angle P occupied by the pitch of the claw pole in the peripheral direction and the output torque shown in the first embodiment of FIG. 1,

FIG. 11 is a perspective view of the electric axial flow pump shown in the first embodiment of FIG. 1 to both ends of which pipes are connected shown in the first embodiment of FIG. 1,

FIG. 12 is a perspective view of the electric axial flow pump for composing vacuum tweezers with the opening on the suction side connected to the suction section shown in the first embodiment of FIG. 1,

FIG. 13 is a cross sectional view of the rotor of the electric axial flow pump relating to the second embodiment of the present invention in the vertical plane,

FIG. 14 is a cross sectional view of the electric axial flow pump in the direction of the rotary shaft relating to the third embodiment of the present invention, wherein to the flow generation section 2, a front view is applied to provide easy understanding,

FIG. 15 is a cross sectional view of the electric axial flow pump in the direction of the rotary shaft relating to the fourth embodiment of the present invention, wherein to the flow generation section 2, a front view is applied to provide easy understanding,

FIG. 16 is a cross sectional view of the electric axial flow pump in the direction of the rotary shaft relating to the fifth embodiment of the present invention, wherein to the flow generation section 2, a front view is applied to provide easy understanding,

FIG. 17(a) is a side view of the electric axial flow pump relating to the sixth embodiment of the present invention and FIG. 17(b) is a cross sectional view in the direction C-C shown in FIG. 17(a), wherein to the flow generation section 2, a front view is applied to provide easy understanding,

FIG. 18(a) is a side view of the electric axial flow pump relating to the seventh embodiment of the present invention and FIG. 18(b) is a cross sectional view in the direction D-D shown in FIG. 18(a), wherein to the flow generation section 2, a front view is applied to provide easy understanding,

FIG. 19(a) is a side view of the electric axial flow pump relating to the eighth embodiment of the present invention and FIG. 19(b) is a cross sectional view in the direction E-E shown in FIG. 19(a), wherein to the flow generation section 2, a front view is applied to provide easy understanding,

FIG. 20(a) is a side view of the electric axial flow pump relating to the ninth embodiment of the present invention and FIG. 20(b) is a cross sectional view in the direction F-F shown in FIG. 20(a).

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, by referring to the accompanying drawings, an embodiment of the electric axial flow pump relating to the present invention will be explained.

Embodiment 1

As shown in FIGS. 1(a) and 1(b), an electric axial flow pump 1 relating to the first embodiment of the present invention has a stator 6 having field coils 10U, 10V, and 10W. Further, the electric axial flow pump 1 has a rotor 3 including a cylindrical hollow shaft 4 having openings 21A and 21B at both ends surrounded by the stator 6 and magnets 5 fixed around the hollow shaft 4. Furthermore, the electric axial flow pump 1 has a flow generation section 2 which is fixed inside the hollow shaft 4, rotates integrally with the rotor 3 when the field coils 10U, 10V, and 10W are excited, thereby generates flow of a fluid 15 inside the hollow shaft 4. The flow generation section 2 lets the fluid 15 flow by rotation and the fluid 15, for example, flows in from the opening 21B at one end of the hollow shaft 4, flows from the opening 21B up to the opening 21A at the other end of the hollow shaft 4 in the direction a rotary shaft 23 of the rotor 3, and flows out from the opening 21A. The flow of the fluid 15 meets the requirements of the axial flow pump.

According to the electric axial flow pump 1, inside the hollow shaft 4 composing the rotor 3, the flow generation section 2 is installed, so that outside the stator 6 surrounding the rotor 3, there is no need to install an auxiliary section such as a pipe and for the rotor 3 and stator 6, before and behind the rotor 3 in the direction of the rotary shaft 23, there is no need to install an auxiliary section such as a pipe. Therefore, the electric axial flow pump can be miniaturized. Further, the flow generation section 2 is installed inside the hollow shaft 4, so that the outside diameter of the shaft of the so-called rotor 3 is increased, thus it is considered to be contrary to miniaturization, though to increase the torque for rotating the rotor 3, it is necessary to fix the magnets 5 onto the outer periphery of the rotor 3 having a large outside diameter and make the radius of rotation of the magnets 5 larger, and an area not narrow is reserved conventionally inside the magnets 5, so that it is not contrary to miniaturization. Inversely, in the electric axial flow pump 1, by reserving a large radius of rotation of the magnets 5, the volume of the flow generation section 2 can be reserved large, so that the torque for rotating the rotor 3 can be increased and the flow rate of the fluid 15 can be increased.

The stator 6 is composed of a plurality of stators 6U, 6V, and 6W arranged in the direction of the rotary shaft 23 of the rotor 3. Alternating currents different in phase are impressed to the respective field coils 10U, 10V, and 10W of the plurality of stators 6U, 6V, and 6W, thus the rotor 3 rotates. Particularly, as shown in FIG. 1(b), the three stators 6U, 6V, and 6W are linked and arranged in the direction of the rotary shaft 23, thus to the field coils 10U, 10V, and 10W of the respective stators 6U, 6V, and 6W, the respective different phases of a three-phase AC power source can be connected one by one, and by this arrangement and connection, the three stators 6U, 6V, and 6W are arranged in the peripheral direction by shifting 120° by 120° at an electrical angle, thus the electric axial flow pump 1 can be driven by the three-phase AC power source.

The respective stators 6U, 6V, and 6W are preferably claw pole stators. The respective stators 6U, 6V, and 6W are composed of stator magnetic cores 7U, 7V, and 7W and the circular field coils 10U, 10V, and 10W wound round the stator magnetic cores 7U, 7V, and 7W. Between the stator magnetic cores 7U, 7V, and 7W and the rotor 3, a gap is formed and the stator magnetic cores 7U, 7V, and 7W are supported by a stator frame 8.

The respective stator magnetic cores 7U, 7V, and 7W are composed of a first claw pole core 11A and a second claw pole core 11B. The first claw pole core 11A is composed of a claw pole 12A opposite to the magnets 5, a circular yoke section 13 extending at right angles from one end of the claw pole 12A to the outside diameter side, and an outer-peripheral side yoke 14 extending in the same direction as that of the claw pole 12A from the circular yoke section 13. Similarly, the second claw pole core 11B is composed of a claw pole 12B opposite to the magnets 5, the circular yoke section 13 extending at right angles from the claw pole 12B to the outside diameter side, and the outer-peripheral side yoke 14 extending in the same direction as that of the claw pole 12B from the circular yoke section 13.

As mentioned above, the stators 6U, 6V, and 6W which are claw pole stators are shaped so as to be bent extending from the circular yoke section 13 to the claw poles 12A and 12B, so that the excessive space extending in the direction of the rotary shaft 23 such as the end portion of a slot type field coil which is not a claw pole stator can be eliminated and the stators 6U, 6V, and 6W can be shortened in the length in the direction of the rotary shaft 23.

On the outer periphery of the stator 6, the stator frame 8 is arranged. The stator frame 8 is in the cylindrical shape along the stator 6 and fixes the stator 6. Before and behind the rotor 3 and stator 6 in the direction of the rotary shaft 23, inside the stator frame 8, a pair of bearings 9A and 9B in the circular ring shape is installed. The bearings 9A and 9B support rotatably the rotor 3 and the inside diameters of the bearings 9A and 9B are larger than the inside diameter of the hollow shaft 4. Therefore, the openings 21A and 21B of the hollow shaft 4 are not covered by the bearings 9A and 9B. And, the openings 22A and 22B at both ends of the stator frame 8 and the openings 21A and 21B at both ends of the hollow shaft 4 can be arranged on one straight line. For example, the flow-in direction in which the fluid 15 flows in from the opening 22B into the opening 21B and the flow-out direction in which it flows out from the opening 21A into the opening 22A can be made the same direction. The directions are the same, so that when the hollow shaft 4 is inserted into the route of the existing pipe such as the cooling circuit used in an automobile or a portable personal computer, the electric axial flow pump can be connected to the route, so that the degree of freedom of design of the cooling circuit can be enhanced.

The flow generation section 2 includes a fin 16, a pillar 17, and a metal fitting 18. It may be considered that the fin 16 and pillar 17 compose a propeller. The fin 16 is spirally arranged and fixed around the pillar 17. The pillar 17 is fixed to the hollow shaft 4 by the fitting 18 so as to make the rotary shaft 23 coincide with the central axis of the pillar 17. The fin 16 and pillar 17 rotate integrally with the rotor 3 and move the fluid 15 in the direction of the rotary shaft 23. The pillar 17 is installed on the rotary shaft 23, and the fin 16 is arranged around it, and the diameter thereof slowly increases in the direction of the rotary shaft 23. The direction in which the thickness increases coincides with the flow direction of the fluid 15. As the fluid 15 flows, the thickness of the pillar 17 at the position of the flow destination increases, thus the flow space of the fluid 15 between the hollow shaft 4 and the pillar 17 is narrowed, so that the fluid 15 is compressed as it flows. The compression of the fluid 15 may be also caused by the centrifugal force acting on the fluid 15 rotating in correspondence with the rotation of the rotor 3. Further, the pitch of the fin 16 spirally wound round the pillar 17 is slowly narrowed in the flow direction of the fluid 15, thus the fluid 15 can be compressed. As mentioned above, by compressing the fluid 15, the compressed fluid 15 can be finally discharged from the opening 21A into the opening 22A where the non-compressed fluid 15 exist. A pumping function for causing a pressure difference to the fluid 15 in the direction of the rotary shaft 23 like this in correspondence with the rotation of the rotor 3 is developed. Such a pumping function appears remarkably when the fluid 15 is a compressive fluid like air.

As shown in FIG. 2, on the outer peripheral surface of the hollow shaft 4 of the rotor 3, a plurality of magnets 5 are arranged in the circumferential direction. Each of the magnets 5 is arranged so as to be different in the polarity direction from the neighboring magnets 5. The magnets 5 are preferably a permanent magnet and particularly preferable a rare-earth magnet. When permanent magnets are used, supply of power is not required, and there is no need to wire the rotor 3, and when rare-earth magnets are used, a high magnetic flux density can be obtained.

In the stator 6, the stators 6U, 6V, and 6W have the same structure, so that the stator 6W will be then explained in detail.

As shown in FIGS. 3 and 4, the stator 6W is structured so as to hold the circular ring-shaped field coil 10W between the circular ring-shaped first claw pole core 11A and the second claw pole core 11B. On the inner peripheral surface of the first claw pole core 11A, a plurality of claw poles 12A (12 poles) are formed at even intervals in the peripheral direction. Similarly, on the inner peripheral surface of the second claw pole core 11B, a plurality of claw poles 12B (12 poles) are formed at even intervals in the peripheral direction. The first claw pole core 11A and second claw pole core 11B have the same structure except that they are different in the position where they are arranged when holding.

As shown in FIG. 4, in the stator magnetic core 7W, the circular ring-shaped end faces of the outer-peripheral side yoke 14 of the first claw pole core 11A and second claw pole core 11B are arranged so as to be overlaid on each other and between the plurality of claw poles 12A, the claw poles 12B are arranged so as to be meshed with each other one by one. By this mesh, pole faces 12F of 24 claw poles 12A and 12B arranged on the same circumference centering on the rotary shaft 23 are formed along the peripheral surface of the rotor 3.

The first claw pole core 11A and second claw pole core 11B have the same structure, so that the first claw pole core 11A will be explained in detail. FIGS. 5, 6, and 7 respectively show a bottom view, a top view, and a cross sectional view of the first claw pole core 11A. For the second claw pole core 11B, the claw pole 12A in the explanation on the claw pole 12A may be replaced with the claw pole 12B.

The first claw pole core 11A, including the claw pole 12A, is preferably formed by compacting magnetic powder. Furthermore, magnetic powder is preferably insulating-coated magnetic powder (iron powder). Magnetic powder with an average maximum width of 20 to 150 μm can be used. Further, as insulating coating, an oxide film with magnetic powder coated which is an inorganic oxide is acceptable and the film thickness is preferably several tens nm or less. By use of insulating-coated magnetic powder, in the first claw pole core 11A of the claw pole 12A, an eddy current loss is caused hardly and the output density of the electric axial flow pump 1 can be improved. Further, magnetic powder is compacted by a punch of the die assembly, so that compared with a one structured by laminating a silicon steel plate, a complicated magnetic pole structure can be obtained. And, since the first claw pole core 11A and second claw pole core 11B are in the same shape, by compacting magnetic powder by the same die, the first claw pole core 11A and second claw pole core 11B in the same shape can be formed easily.

When compacting magnetic powder, thereby forming the first claw pole core 11A, the magnetic powder is compacted by the die, though the compacting direction thereof is the direction of the rotary shaft 23 in which the claw pole 12A extends. At this time, the punch for compacting the first claw pole core 11A, to prevent the punch from buckling, the sectional area of the punch in proportion to the length of the first claw pole core 11A, which is a compacted piece, in the direction of the rotary shaft 23 is necessary.

In other words, on the basis of a length L1 (refer to FIG. 7) of the claw pole 12A when the length of the first claw pole core 11A in the direction of the rotary shaft 23 is maximized, the sectional area of the punch must be decided. And, since the sectional area of the punch is necessary, at an extending end 12T (refer to FIG. 6) of the claw poles 12A and 12B in the axial direction, a flat surface orthogonal to the direction of the rotary shaft 23 is necessary. The area of the flat surface is the sectional area of the punch and when the length L1 of the claw pole 12A in the direction of the rotary shaft 23 is increased, must be increased in proportion to the length L1.

In a compacted piece produced by compacting magnetic powder, to obtain a high magnetic characteristic, a compacting pressure of about 10 ton/cm² is necessary and the sectional area of the punch corresponding to it is necessary at the extending end 12T of the claw pole 12A in the axial direction. And, to preserve the sectional area of the punch, the results of trial manufacture show that it is necessary to control a thickness H2 (refer to FIG. 7) in the radial direction of the claw pole 12A at the extending end 12T in the axial direction to at least 2 mm or more, thereby preserve the sectional area of the punch.

Furthermore, when ejecting the first claw pole core 11A compacted at the compacting pressure of 10 ton/cm² from the die, a tapered surface 12K inclined at a draft taper angle θ from the direction of the rotary shaft 23 is necessary and it is necessary in the claw pole 12A to form the draft taper angle θ tapering from the base thereof to the extending end 12T in the axial direction. The results of trial manufacture show that to compact magnetic powder and draw the first claw pole core 11A from the die, a draft taper angle θ of 8° or more is necessary. When the draft taper angle θ is as large as possible, the drawing operation can be performed easily. However, when the draft taper angle θ is increased, the area of the magnetic pole surface 12F of the claw pole 12A is reduced and the magnetic characteristic is lowered, so that the inventors confirm that the draft taper angle θ is preferably 10° or less hardly affecting the magnetic characteristic. Therefore, it is found that the draft taper angle θ is preferably set between 8° and 10°.

Further, a ratio of L1/L2 of the maximum length L1 of the first claw pole core 11A in the direction of the rotary shaft 23 to the minimum length L2, in relation to the sectional area of the punch, the number of poles of the motor which is the sum of the numbers of the first claw poles 12A and second claw poles 12B, and the draft taper angle θ, has an upper limit and when the number of poles of the motor is 50 or less, is desirably 5 or less. Meanwhile, the maximum length L1 of the first claw pole core 11A in the direction of the rotary shaft 23 is measured in the claw pole 12A and the minimum length L2 is measured in the circular yoke section 13.

The first claw pole core 11A is formed by compacting of magnetic powder as mentioned above, thus the magnetic powder can be compacted at a high compacting pressure from the base of the claw pole 12A to the extending end 12T in the axial direction, so that the density of the first claw pole core 11A including the claw pole 12A can be increased to 7.5 g/cm³ or more.

The stator 6W is formed using the first claw pole core 11A and second claw pole core 11B prepared by various materials as shown in FIG. 8 and the magnetizing characteristics of the respective stators 6W are compared and shown in FIG. 8. From the comparison of the magnetization characteristics for the various materials, the aforementioned matter can be backed up quantitatively. Further, a powder core 1 shown in FIG. 8 measures the stator 6W using the first claw pole core 11A and second claw pole core 11B for compacting magnetic powder so as to control the density to 7.3 g/cm³. The SPCC (Japanese Industrial Standard) measures the stator 6W using the first claw pole core 11A and second claw pole core 11B for forming a cold rolled steel plate SPCC. A powder core 2 measures the stator 6W using the first claw pole core 11A and second claw pole core 11B for compacting magnetic powder so as to control the density to 7.5 g/cm³. The 35A300, 50A1300, and SS400 measure the stator 6W using the first claw pole core 11A and second claw pole core 11B for respectively forming silicon steel plates 35A300, 50A1300, and SS400.

The powder core 1, compared with the SPCC, 35A300, 50A1300, and SS400 (Japanese Industrial Standard), may be considered that a magnetic flux density B (T) is low as a whole and the magnetizing characteristic is deteriorated. On the other hand, the powder core 2 may be considered that a magnetic flux density B (T) equivalent to that of the SPCC or SS400 is obtained as a whole and the magnetizing characteristic is equivalent to that of the SPCC or SS400.

Therefore, when the stator 6W using the first claw pole core 11A and second claw pole core 11B for compacting magnetic powder so as to control the density of the powder core 1 to 7.3 g/cm³ is used for the electric axial flow pump 1, the magnetic flux density B is low and the magnetic characteristic is deteriorated, so that when the magnets 5 (refer to FIG. 2) having a high residual magnetic flux density are used in the magnetic field, reduction in the pump characteristics may be expected such that the output torque is reduced due to saturation of the magnetic flux density B. Therefore, for the first claw pole core 11A and second claw pole core 11B, the first claw pole core 11A and second claw pole core 11B for compacting magnetic powder so as to control the density of the powder core 2 to 7.5 g/cm³ are used.

On the other hand, the SPCC, 35A300, 50A1300, and SS400 are formed by bending a cold rolled steel sheet and a silicon steel sheet, so that an eddy current loss is caused to the claw pole 12A, circular yoke section 13, and outer peripheral side yoke 14, so that it may be considered that if the input power is fixed, to ensure the magnetic characteristic, high-speed rotation may not be performed. According to the first claw pole core 11A and second claw pole core 11B for compacting magnetic powder so as to control the density of the powder core 2 to 7.5 g/cm³, the magnetic powder is mutually insulated from each other by insulating coating, so that an eddy current loss is caused hardly and there is no effect of the magnetostriction due to bending forming.

Furthermore, as the electric axial flow pump 1, it is desired to ensure high magnetomotive force by using the magnets 5 having a high residual magnetic flux density for the rotor 3 and to install the first claw pole core 11A and second claw pole core 11B for effectively using the magnetomotive force, so that firstly rare-earth magnets of permanent magnets are used for the magnets 5, and the magnetic flux density is controlled between 1.2 T and 1.4 T, thus high magnetomotive force is ensured. Next, to install the first claw pole core 11A and second claw pole core 11B capable of effectively using the high magnetic flux density (magnetomotive force), the dimensional relationship between the first claw pole core 11A and the second claw pole core 11B is found by the examination indicated below.

FIG. 9 shows, when a draft taper angle θ of 8° shown in FIG. 7, a thickness H2 of 2 mm, and a ratio of 5 of the length L1 to the length L2 are set as fixed conditions, the calculation results of the relationship between the number M of the claw poles when inside diameters D (mm) (refer to FIG. 5) of the first claw pole core 11A and second claw pole core 11B are changed and the output torque (N·m) of the electric axial flow pump 1. It is found that when the inside diameter D is decided uniquely, the output torque is maximized at a specific number of poles M. The number of poles M when the output torque is maximized depends on the inside diameter D and in the relational expression (M=a·D) between the inside diameter D and the number of poles M expressed by a dotted line Peak shown in FIG. 9, it is found that when a coefficient a (mm⁻¹) is 0.4 or so, the output torque is maximized. And, in the relational expression (M=a·D), it is found that when the coefficient a (mm⁻¹) is within the range from 0.35 to 0.5 (0.35≦a (mm⁻¹)≦0.5), the output torque is maximized.

Next, from the above results, the inside diameter D and number of poles M are set so as to maximize the output torque and particularly using the electric axial flow pump in which the number of poles is set to 24 and 32, the average width angle T (refer to FIG. 6) in the peripheral direction of the first claw pole core 11A of the claw pole 12A is examined.

In FIG. 10, the calculation results of the relationship between the average width angle T in the peripheral direction of the claw pole 12A and the output torque are shown. In the claw pole 12A of a draft taper angle θ of 8°, as a mean value of a maximum width angle Tmax and a minimum width angle Tmin occupied in the peripheral direction of the first claw pole core 11A, the average width angle T in the peripheral direction is obtained. Further, a pitch angle P is obtained as an angle occupied in the peripheral direction by the pitch of the claw pole 12A equivalent to one cycle of the electric angle. From the viewpoint of the relationship between a ratio of T/P of the pitch angle P to the average width angle T in the peripheral direction and the output torque, it is found that for both 24 poles and 32 poles, when the ratio T/P is within the range form 0.4 to 0.45, the output torque is maximized. The reason may be considered that when the average width angle T in the peripheral direction of the claw pole 12A is small, the magnetic flux on the side of the rotor 3 cannot interlink sufficiently with the field coil 10W and when it is excessively large inversely, the interval between the claw pole 12A and its neighboring claw pole 12B is narrowed, and the leakage flux from the claw pole 12A to its neighboring claw pole 12B is increased, and the output torque is lowered. When the claw pole 12A can be designed freely, maximization of the output torque under other conditions may be considered, though when the aforementioned restriction is imposed on the claw pole 12A, when the ratio T/P of the average width angle T in the peripheral direction of the claw pole 12A to the pitch angle P equivalent to one cycle of the electric angle is within the range from 0.4 to 0.45, the output torque is obtained stably. Further, for the numbers of poles M other than 24 poles and 32 poles, the similar results are obtained.

The first claw pole core 11A and second claw pole core 11B are structured as described above, thus the pumping efficiency of the electric axial flow pump 1 can be improved.

As shown in FIG. 11, the electric axial flow pump 1, by connecting the openings 22A and 22B to a pipe 24 of the cooling circuit used for an automobile or a portable personal computer, can circulate cooling water through the pipe 24. The stator frame 8 is cylindrical, so that if the outside diameter of the stator frame 8 is made equal to the inside diameter of the pipe 24, the electric axial flow pump 1 can be connected easily to the pipe 24. Therefore, the outside diameter of the stator frame 8 is made smaller than the outside diameter of the pipe 24, so that the electric axial flow pump 1 can be stored in the area on the extension of the pipe 4. In the electric axial flow pump 1, the flow-in direction of cooling water into the opening 22B and the flow-out direction of cooling water from the opening 22A are the same, so that it can be easily inserted into the route of the existing pipe of the cooling circuit used for an automobile or a portable personal computer.

As shown in FIG. 12, in the electric axial flow pump 1, a suction section 28 can be connected directly to the opening 22B on the suction side. The electric axial flow pump 1 functions as a vacuum pump, so that the suction section 28 is decompressed and the suction section 28 sucks in an electronic part 29. The electric axial flow pump 1 and suction section 28 are directly connected like this, thus they can compose portable vacuum tweezers.

Embodiment 2

FIG. 13 is a cross sectional view of the rotor 3 in the radial direction of the electric axial flow pump 1 relating to the second embodiment of the present invention. The rotor 3 of this embodiment, compared with the rotor 3 shown in FIG. 2, is different in additional installation of a powder core 19 between the hollow shaft 4 and the magnets 5. The powder core 19 functions as a rotor backyoke. The magnets 5 and powder core 19 are formed by compacting powder material. By formation by a powder material, by a high electrical resistance between powders, the eddy current generated between the hollow shaft 4 and the magnets 5 can be reduced. And, the rotational speed of the rotor 3 can be increased.

The magnets 5 are produced mainly from a binder and magnet powder. The powder core 19 is produced mainly from a binder and soft magnetic powder.

Further, at least one surface of the magnetic pole of each of the magnets 5 is joined mechanically to the powder core 19. The mechanical joint is caused during the process of compacting of a powder material. Hereinafter, the compacting process will be explained. Firstly, the magnets 5 are compacted temporarily by compacting for each segment. During the temporary compacting, they are magnetized by the magnetization field and are given anisotropy. Next, using the hollow shaft 4 as a part of the die, for the powder core 19 and temporarily compacted magnets 5, real compacting for simultaneously applying pressure in the compact direction in the direction of the rotary shaft 23 is performed. By this real compacting, the hollow shaft 4, powder core 19, and magnets 5 are compacted integrally and the magnets 5 and powder core 19 are joined mechanically. The rotor 3 is formed by a powder material, thus the same effect as that shown in FIG. 1 can be obtained and furthermore, the mechanical structure of the rotor 3 can be formed in a shape of a higher degree of freedom.

Embodiment 3

FIG. 14 is a cross sectional view of the electric axial flow pump 1 relating to the third embodiment of the present invention in the direction of the rotary shaft 23. The difference of the electric axial flow pump 1 relating to the third embodiment shown in FIG. 14 from the electric axial flow pump 1 shown in FIG. 1 is that the stator 6 is composed of two stators 6A and 6M instead of the three stators 6U, 6V, and 6W. In FIG. 14, to the same components as those shown in FIG. 1, the same numerals are assigned and the duplicated explanation will be omitted. The stators 6A and 6M have the same structure as that of the stator 6W. The stator 6A is composed of a stator magnetic core 7A and a field coil 10A and the stator 6M is composed of a stator magnetic core 7M and a field coil 10M. The stator magnetic cores 7A and 7M have the same structure as that of the stator magnetic core 7W. The field coils 10A and 10M have the same structure as that of the field coil 10W. The stator magnetic cores 7A and 7M respectively have the first claw pole core 11A and second claw pole core 11B.

The electric axial flow pump 1 of the third embodiment additionally has a phase splitting section 25 for generating a second single-phase alternating current obtained by shifting the phase of a first single-phase alternating current of a single-phase AC source 26 by a predetermined angle of about 90°. The phase splitting section 25 can be composed of a capacitor and may include a coil. The phase splitting section 25 connects the first single-phase alternating current and second single-phase alternating current respectively to the field coils 10A and 10M. By this connection, the stators 6A and 6M are arranged by shifting by a predetermined phase at an electrical angle in the peripheral direction, for example, when the phase splitting section 25 is composed of a capacitor, by shifting by about 90° and to the field coils 10A and 10M, a single-phase power source having a phase difference angle of 90° at an electrical angle is connected. By use of such a constitution, the electric axial flow pump 1 driven by the single-phase AC source 26 can be provided.

Embodiment 4

FIG. 15 is a cross sectional view of the electric axial flow pump 1 relating to the fourth embodiment of the present invention in the direction of the rotary shaft 23. The difference of the electric axial flow pump 1 relating to the fourth embodiment shown in FIG. 15 from the electric axial flow pump 1 shown in FIG. 1 is that the stator 6 is increased in the group of the three stators 6U, 6V, and 6W from one group to two groups of S1 and S2. In FIG. 15, to the same components as those shown in FIG. 1, the same numerals are assigned and the duplicated explanation will be omitted. To the respective field coils 10U of the two stators 6U, the U-phase voltage of the three-phase power source is impressed, and to the respective field coils 10V of the two stators 6V, the V-phase voltage of the three-phase power source is impressed, and to the respective field coils 10W of the two stators 6W, the W-phase voltage of the three-phase power source is impressed, thus the electric axial flow pump 1 can be driven at two-fold torque of the electric axial flow pump 1 shown in FIG. 1 and the electric axial flow pump 1 of higher output can be provided.

Embodiment 5

FIG. 16 is a cross sectional view of the electric axial flow pump 1 relating to the fifth embodiment of the present invention in the direction of the rotary shaft 23. The difference of the electric axial flow pump 1 of the fifth embodiment shown in FIG. 16 from the electric axial flow pump 1 of the third embodiment shown in FIG. 14 is that the stator 6 is increased in the group composed of the stators 6A and 6M from one group to two groups of S1 and S2 and can be driven by a two-phase alternating current. In FIG. 16, to the same components as those shown in FIG. 14, the same numerals are assigned and the duplicated explanation will be omitted. To the respective field coils 10A of the two stators 6A, the second single-phase alternating current obtained by shifting the phase of the first single-phase alternating current of the single-phase AC source 26 by the predetermined angle by the phase splitting phase 25 is supplied, and the first single-phase alternating current is supplied to the field coils 10M of the two stators 6M, thus the electric axial flow pump 1 can be driven at two-fold torque of the electric axial flow pump 1 shown in FIG. 14 and the electric axial flow pump 1 of higher output can be provided.

Embodiment 6

FIGS. 17(a) and 17(b) are a side view of the electric axial flow pump 1 relating to the sixth embodiment of the present invention and a cross sectional view thereof in the direction of the rotary shaft 23. The difference of the electric axial flow pump 1 of the sixth embodiment shown in FIG. 17 from the electric axial flow pump 1 shown in FIG. 1 is that in the flow generation section 2, the metal fitting 18 is removed and the fin 16 is fixed directly to the hollow shaft 4 of the rotor 3. To the same components as those shown in FIG. 1, the same numerals are assigned and the duplicated explanation will be omitted. In correspondence with unnecessity of the metal fitting 18, the openings 21A and 21B of the hollow shaft 4 can be widened and the flow path resistance to the fluid 15 can be reduced. Further, the fin 16 is not supported by the pillar 17 at one end thereof but supported by the pillar 17 and hollow shaft 4 at both ends thereof, so that the resistance to load of the fin 16 to the fluid 15 can be increased. Inversely, the fin 16 can be thinned to a thickness for obtaining a necessary resistance to load and a faster rotation can be realized.

Embodiment 7

FIGS. 18(a) and 18(b) are a side view of the electric axial flow pump 1 relating to the seventh embodiment of the present invention and a cross sectional view thereof in the direction of the rotary shaft 23. The difference of the electric axial flow pump 1 of the seventh embodiment shown in FIG. 18 from the electric axial flow pump 1 shown in FIG. 1 is that in the flow generation section 2, the pillar 17 and metal fitting 18 are removed and both ends of the fin 16 in the radial direction are respectively fixed directly to the hollow shaft 4 of the rotor 3. Further, the fin 16 is arranged on the rotary shaft 23 and is screwed to the rotary shaft 23 as a fixing shaft. To the same components as those shown in FIG. 1, the same numerals are assigned and the duplicated explanation will be omitted. In correspondence with removal of the pillar 17 and metal fitting 18, the flow path of the fluid 15 in the hollow shaft 4 can be widened and the flow path resistance can be reduced. Further, the fin 16 is supported by the hollow shaft 4 at both ends thereof in the radial direction, so that the resistance to load of the fin 16 to the fluid 15 is increased.

Embodiment 8

FIGS. 19(a) and 19(b) are a side view of the electric axial flow pump 1 relating to the eighth embodiment of the present invention and a cross sectional view thereof in the direction of the rotary shaft. The difference of the electric axial flow pump 1 of the eighth embodiment shown in FIG. 19 from the electric axial flow pump 1 shown in FIG. 1 is that in the flow generation section 2, the so-called propeller is installed. The flow generation section 2 shown in FIG. 1 may be considered as a kind of propeller of one fin 16, though in the eighth embodiment, a plurality of propellers having a plurality of fins 16 are installed in the hollow shaft 4. Further, the propellers can be fixed not only in the neighborhood of the openings 21A and 21B in the hollow shaft 4 but also at an optional position such as the central part. To fix each propeller at an optional position, the fin 16 of the propeller is fixed directly to the hollow shaft 4. The detailed structure of each propeller, for example, the number of fins 16, inclination, and shape can be changed depending on the properties of the fluid 15. For example, when the fluid is a liquid, the structure of screw can be applied. The rotor 3 rotates and the propellers rotate integrally with the rotor 3, thus an eddy of the fluid 15 is formed round the rotary shaft as a central axis and the fluid 5 moves along the flow of the eddy.

Embodiment 9

FIGS. 20(a) and 20(b) are a side view of the electric axial flow pump 1 relating to the ninth embodiment of the present invention and a cross sectional view thereof in the direction of the rotary shaft. The difference of the electric axial flow pump 1 of the ninth embodiment shown in FIG. 20 from the electric axial flow pump 1 shown in FIG. 1 is that in the flow generation section 2, slits 27 are formed inside the hollow shaft 4 in the twisted direction to the direction of the rotary shaft. The rotor 3 rotates and the slits 27 united with the hollow shaft 4 of the rotor 3 rotate, thus an eddy of the fluid 15 is formed round the rotary shaft as a central axis and the fluid 15 moves along the flow of the eddy. 

1. An electric axial flow pump comprising: a stator having a field coil, a rotor including a cylindrical hollow shaft having open ends surrounded by the stator and a plurality of magnets fixed around the hollow shaft, and a flow generation section fixed inside the hollow shaft for rotating integrally with the rotor when the field coil is excited, thereby generating flow of a fluid inside the hollow shaft.
 2. The electric axial flow pump according to claim 1, wherein the stator is a claw pole type stator.
 3. The electric axial flow pump according to claim 2, wherein the stator has a plurality of claw poles formed by compacting insulating-coated magnetic powder on the inner peripheral surface and a circular ring-shaped stator magnetic core for covering the field coil, and the field coil is a circular coil mounted inside the stator magnetic core.
 4. The electric axial flow pump according to claim 1, wherein the flow generation section has a fin for rotating integrally with the rotor and moving the fluid in a direction of a rotary shaft of the rotor.
 5. The electric axial flow pump according to claim 4, wherein the fin is fixed directly to the rotor.
 6. The electric axial flow pump according to claim 4, wherein the flow generation section has a pillar installed on the rotary shaft for slowly increasing thickness in the direction of the rotary shaft, and the fin is arranged around the pillar.
 7. The electric axial flow pump according to claim 1, wherein the flow generation section has a propeller for rotating integrally with the rotor and moving the fluid in a direction of a rotary shaft of the rotor.
 8. The electric axial flow pump according to claim 1, wherein the flow generation section has slits formed inside the hollow shaft in a twisted direction to the direction of the rotary shaft of the rotor.
 9. The electric axial flow pump according to claim 1, further comprising: a cylindrical stator frame arranged on an outer periphery of the stator for fixing the stator and a pair of bearings in a circular ring shape installed inside the stator frame before and behind the rotor for supporting rotatably the rotor, wherein inside diameters of the bearings are larger than an inside diameter of the hollow shaft.
 10. The electric axial flow pump according to claim 9, wherein openings at both ends of the stator frame and the openings at the both ends of the hollow shaft are arranged on one straight line and a flow-in direction of the fluid and a flow-out direction thereof are the same direction.
 11. The electric axial flow pump according to claim 1, wherein a plurality of the stators are installed in a direction of a rotary shaft of the rotor and to the respective field coils of a plurality of the stators, polyphase AC voltages different in phase are impressed.
 12. The electric axial flow pump according to claim 1, wherein so as to permit respective different phases of a three-phase AC power source to be connected one by one to the field coils of the respective stators, the stators are shifted 120° by 120° at an electrical angle and three the stators are arranged in a direction of a rotary shaft of the rotor.
 13. The electric axial flow pump according to claim 12, wherein two or more groups of the three stators are installed in the direction of the rotary shaft.
 14. The electric axial flow pump according to claim 1, further comprising: a phase splitting section for generating a second single-phase alternating current obtained by shifting a phase of a first single-phase alternating current of a single-phase AC source by 90°, wherein: so as to permit the first single-phase alternating current and the second single-phase alternating current to be connected one by one to the field coils of the respective stators, the stators are shifted by 90° at an electrical angle and two the stators are arranged in a direction of a rotary shaft.
 15. The electric axial flow pump according to claim 14, wherein two or more groups of the two stators are installed in the direction of the rotary shaft.
 16. The electric axial flow pump according to claim 1, wherein the rotor has a powder core installed between the hollow shaft and the magnets.
 17. The electric axial flow pump according to claim 3, wherein: a thickness of the claw poles in a radial direction is 2 mm or more, the claw poles have a flat surface perpendicular to a direction of a rotary shaft at an extending end of the rotor in the direction of the rotary shaft and a draft taper inclined at an angle within a range from 8° to 10° to the direction of the rotary shaft tapering from a base of the claw poles to the extending end, and a ratio of a length of the claw poles in the direction of the rotary shaft to a minimum thickness of the stator magnetic core in the direction of the rotary shaft is less than
 5. 18. The electric axial flow pump according to claim 17, wherein assuming the relationship between a number M of the claw poles and an inside diameter D of the stator as M=a·D, a coefficient a is between 0.35 and 0.5.
 19. The electric axial flow pump according to claim 17 or 18, wherein a ratio of T/P of an average width angle T of a maximum width angle and a minimum width angle occupied by the claw poles in a peripheral direction of the stator magnetic core to a pitch angle P occupied by a pitch of the claw pole cores in the peripheral direction is between 0.4 and 0.45.
 20. The electric axial flow pump according to claim 3, wherein density of the stator magnetic core is 7.5 g/cm³ or more. 